Monel K500 – Chemical Composition, Equivalents & Products
Monel K500 (also written K-500; UNS N05500, WNR 2.4375) is a nickel-copper alloy with additions of aluminium and titanium. It combines the corrosion resistance of Monel 400 – in seawater, brines, alkalis and many acids – with much greater strength and hardness, achieved by age hardening. After ageing, its yield strength is roughly three times that of annealed Monel 400, and it remains non-magnetic down to low temperatures.
Giriraj Impex supplies Monel K500 – we manufacture flanges, fittings, bars and fasteners, and stock and supply pipes, tubes, plates and sheets – mainly as round bars, forgings, fasteners and shafts, to ASTM B865 and customer specifications.
Chemical composition
| Alloy | Ni | Cu | Fe | Mn | C | Si | S | Al | Ti |
|---|---|---|---|---|---|---|---|---|---|
| 400 (N04400) | 63.0 min | 28.0–34.0 | 2.5 | 2.0 | 0.3 | 0.5 | 0.024 | – | – |
| K-500 (N05500) | 63.0 min | 27.0–33.0 | 2.0 | 1.5 | 0.25 | 0.5 | 0.01 | 2.30–3.15 | 0.35–0.85 |
Nickel includes cobalt. Limits as given in ASTM B127, B164 and B165 (alloy 400) and B865 (alloy K-500).
The table compares K500 with Monel 400. Aluminium and titanium combine with nickel during ageing to form fine gamma-prime particles that strengthen the alloy without reducing its corrosion resistance.
Mechanical properties
Monel K500 is supplied annealed or hot finished for machining, and is age hardened at around 600 °C for several hours, followed by slow cooling, to reach its full strength. Typical aged bar has a yield strength in the region of 690–760 MPa and a tensile strength of about 1000–1100 MPa, with hardness around 25–35 HRC, depending on size and prior cold work; the exact requirements for each condition and size are set in ASTM B865 and reported on the mill test certificate. For sour service, NACE MR0175 / ISO 15156 sets hardness limits for aged K500.
Equivalent designations
| Designation | Value |
|---|---|
| UNS | N05500 |
| WNR | 2.4375 |
| DIN name | NiCu30Al |
| ASTM bar, rod, wire and forgings | B865 |
| Fasteners | ASTM F467 / F468 |
| Aerospace / military | AMS 4676; QQ-N-286 (historical) |
See the grade equivalent chart.
Monel K500 products we supply
- Monel round bars – ASTM B865, annealed or aged
- Monel fasteners – high-strength K500 studs, bolts and nuts
- Monel flanges – K500 forgings on request
- Monel pipe fittings – machined from K500 bar on request
- Monel pipes and tubes – alloy 400; K500 on enquiry
- Monel sheets and plates – alloy 400; K500 on enquiry
All Monel alloys are on the Monel page.
Where Monel K500 is used
Monel K500 is used for marine pump shafts and impellers, propeller shafts, valve stems and trim, fasteners and springs in seawater; oil-well tools and drill collars, where its non-magnetic property is used for directional-drilling instruments; doctor blades and scrapers in pulp and paper; chains and cables for marine use; and electronic and instrument components that must stay non-magnetic. It is chosen where the corrosion resistance of Monel 400 is needed with the strength of alloy steel.
Monel K500 compared with other alloys
Monel 400 has similar corrosion resistance but much lower strength and is used for piping and vessels. Inconel 718 is stronger still and keeps its strength at high temperature, but costs more. In seawater, super duplex stainless steel shafts are an alternative with similar strength; K500 is preferred where non-magnetic properties or resistance to fouling and pitting in stagnant conditions are wanted.
Machining and heat treatment
Monel K500 is usually rough machined in the annealed or hot-finished condition, then aged, and finish machined or ground after ageing. Ageing causes a slight, predictable dimensional change, so allowance is made in the machining plan. In the aged condition, machining needs rigid set-ups, carbide tools and low speeds. Welding of K500 is possible but is rarely used for structural joints; parts are normally machined from bar or forgings.
Sizes and supply
Monel K500 is supplied in the product forms listed above, in metric and imperial sizes. Because nickel alloys are produced by a limited number of mills and in smaller quantities than stainless steel, availability of each size, the delivery of special sizes and the minimum mill quantities are confirmed with each quotation. Cut lengths, cut plates and machined blanks reduce waste of an expensive alloy and can be supplied on request. Please send the full requirement – grade, specification, product, size, quantity and testing – so that the complete package can be quoted together.
Sour service and hydrogen
In oil and gas service, aged Monel K500 is used within the hardness limits of NACE MR0175 / ISO 15156, which can be supplied on request. In seawater under cathodic protection, high-strength aged K500 can absorb hydrogen and become prone to cracking, particularly in the presence of high hardness or stress concentrations; designs for subsea bolting and shafts should consider this, and hardness controls may be specified.
Documents and inspection
Material is supplied with mill test certificates (MTC) showing heat number, chemical composition, mechanical properties and heat treatment. Third-party inspection is available on request, and positive material identification can be carried out before dispatch. Because nickel alloys look alike, every piece is marked with grade and heat number for traceability through fabrication.
Frequently Asked Questions
Monel K500 (UNS N05500) is an age-hardenable nickel-copper alloy with aluminium and titanium, combining Monel corrosion resistance with high strength.
K500 is age hardened to roughly three times the yield strength of annealed 400, with similar corrosion resistance.
ASTM B865 covers Monel K500 bar, rod, wire, forgings and forging stock.
No. Monel K500 remains non-magnetic down to low temperatures, which is why it is used for drilling instruments.
For marine pump and propeller shafts, valve stems, fasteners, oil-well tools and non-magnetic components.
Monel K500 is WNR 2.4375, NiCu30Al.
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